Air filtration system having a removable diffuser

ABSTRACT

An air filtration system includes a support structure, an enclosure coupled to the support structure and including an air outlet, a filter and a fan operatively coupled to the enclosure, and a diffusion screen configured to cover the air outlet. The diffusion screen includes a screen frame configured to be removably attachable to the enclosure with at least one releasable fastener, and at least a diffusion layer substantially spanning the screen frame to cover the air outlet to provide unidirectional or laminar air flow from the air outlet.

FIELD OF THE DISCLOSURE

The present application generally relates to air filtration systems, andmore particularly, to an air filtration system having a removablediffuser.

BACKGROUND

Air filtration devices are typically used in environments where cleanair having low particulate matter or low gaseous contaminate material isrequired. For example, air filtration systems are used in operatingrooms of hospitals, in hospital rooms where burn patients are treated,in clean rooms such as semiconductor manufacturing facilities, and inany other environment where small particles, certain gaseous materials,or certain contaminants in the surrounding air can be hazardous to aperson's health or disrupt the work being performed or damage theproducts.

Air filtration systems typically include a fan unit that receives airfrom an air input and directs the air with a desired flow rate to afilter unit. The filter unit removes the particulate matter and/orgaseous contaminant material from the air. Air filtration systems mayalso include a diffuser positioned downstream of the filter that canchange flow characteristics of the air. A diffuser can be designed toprovide unidirectional flow, multidirectional flow, laminar flow, orturbulent flow.

Many air filtration systems are of room air cleaner type. They aredesigned to clean air in an entire room or space and can not direct airto a small desired area. The air flow coming out of a typical room aircleaner is turbulent. Such units cannot provide unidirectional air flowto a specific zone to create a localized clean environment.

Many other air filtration systems are ceiling mounted or attached to awork surface. Accordingly, the clean air is directed to a desirablelocation depending on the fixed position and orientation of the airfiltration system. For example, a ceiling mounted air filtration systemwill typically direct the air flow downward. In another example, a workbench can include an air filtration system mounted above the worksurface thereof so that clean air is directed onto the work surface.Such air filtration systems are not portable and can only be used in theenvironment and for the application for which they are designed.Furthermore, most of such air filtration systems do not have diffusersfor providing laminar or unidirectional clean air flow to a localizedzone without containment of the airflow. For those systems that havediffusers, the diffuser can not be easily removed and replaced withanother diffuser. Such removal may be necessary for replacing orcleaning the diffuser, or replacing the filter, or modifying the flowcharacteristics.

Therefore, there exists a need in the art for an air filtration systemwith a removable diffuser that is portable, can be reoriented to provideunidirectional clean air to a desired zone, and has a diffuser materialthat can be easily replaced or cleaned.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments are shown in the drawings. However, it is understoodthat the present disclosure is not limited to the arrangements andinstrumentality shown in the attached drawings, wherein:

FIG. 1 illustrates a perspective view of an air filtration systemconstructed in accordance with the teachings of the present disclosure;

FIG. 2 illustrates a side view of another air filtration systemconstructed in accordance with the teachings of the present disclosure;

FIG. 3 illustrates a side view of another air filtration systemconstructed in accordance with the teachings of the present disclosure;

FIG. 4 illustrates a side view of another air filtration systemconstructed in accordance with the teachings of the present disclosure;

FIG. 5 illustrates a side view of another air filtration systemconstructed in accordance with the teachings of the present disclosure;

FIG. 6 illustrates a side view of another air filtration systemconstructed in accordance with the teachings of the present disclosure;

FIG. 7 illustrates a front perspective view of another air filtrationsystem constructed in accordance with the teachings of the presentdisclosure;

FIG. 8 illustrates a side view of another air filtration systemconstructed in accordance with the teachings of the present disclosure;

FIG. 9 illustrates a perspective view of a diffusion screen constructedin accordance with the teachings of the present disclosure;

FIGS. 10( a) and 10(b) illustrate a perspective view and a perspectiveexploded view, respectively, of a diffusion screen and a correspondingfan and filter constructed in accordance with the teachings of thepresent disclosure;

FIGS. 11( a)-11(d) illustrate perspective views of exemplary diffusionlayer configurations for a diffusion screen constructed in accordancewith the teachings of the present disclosure.

FIG. 12 illustrate a perspective view of a latching mechanism forremovably attaching a diffusion screen to an enclosure in accordancewith the teachings of the present disclosure;

FIGS. 13( a) and 13(b) illustrate side views of two exemplaryconfigurations for the latching mechanism of FIG. 12; and

FIGS. 14( a)-14(c) illustrate side views of three exemplary latchingmechanisms for removably attaching a diffusion screen to an enclosureand filter in accordance with the teachings of the present disclosure:

DETAILED DESCRIPTION

For the purposes of promoting and understanding the principles disclosedherein, reference will now be made to the preferred embodimentsillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope is thereby intended. Such alterations and furthermodifications in the illustrated device and such further applicationsare the principles disclosed as illustrated therein as beingcontemplated as would normally occur to one skilled in the art to whichthis disclosure relates.

In accordance with a principal aspect of the present disclosure, an airfiltration system includes a support structure, an enclosure coupled tothe support structure and including an air outlet, a filter and a fanoperatively coupled to the enclosure, and a diffusion screen configuredto cover the air outlet. The diffusion screen includes a screen frameconfigured to be removably attachable to the enclosure with at least onereleasable fastener, and at least a diffusion layer substantiallyspanning the screen frame to cover the air outlet to provideunidirectional air flow from the air outlet.

In accordance with another principal aspect of the present disclosure, adiffusion screen for an air filtration system having a filter and a fanoperatively coupled to an enclosure for providing air flow from an airoutlet of the enclosure includes a frame and a diffusion layer. Theframe is configured to be removably attached to a perimeter of the airoutlet with at least one releasable fastener. The diffusion layer spansthe frame to cover the air outlet. The diffusion layer is configurableto provide at least unidirectional or laminar flow from the air outlet.

In accordance with another principal aspect of the present disclosure,an air filtration system includes a support structure, an enclosurecoupled to the support structure, the enclosure including an air outlet,a filter and a fan attached to the support structure and operativelycoupled to the enclosure to provide airflow from the air outlet, and adiffusion screen configured to cover the air outlet. The diffusionscreen includes a frame configured to be removably attached to aperimeter of the air outlet with at least one releasable fastener, andat least a diffusion layer spanning the frame to cover the air outlet,the diffusion layer configured to provide at least unidirectional orlaminar flow from the air outlet.

Referring to FIGS. 1-7, several examples of an air filtration system 30constructed in accordance with the teachings of the present disclosureare shown. Each of the air filtration systems 30 includes a supportstructure 32 and an enclosure 34 that is coupled to the supportstructure 32. The enclosure 34 includes an air outlet 36. A filter and afan (not shown) are operatively coupled to the enclosure 34. Each of theair filtration systems 30 also includes a diffusion screen 40 that isconfigured to cover their air outlet 36. The diffusion screen includes ascreen frame 42 that supports at least one diffusion layer 44substantially spanning the screen frame 42. The screen frame 42 and thediffusion layer 44 cover the air outlet 36 and provide unidirectional orlaminar air flow 46 from the air outlet 36.

The filter and the fan (not shown) may be housed in the enclosure 34such that it is adjacent to the air outlet 36. Alternatively, the filterand the fan may be disposed outside the enclosure 34 and in air flowcommunication with the enclosure 34. The filter and the fan (not shown)are referred to herein as a single unit. However, one of ordinary skillin the art will appreciate that the filter and the fan (not shown) canalso be two independent structures that may only be in air flowcommunication. Accordingly, the filter and the fan (not shown) that isdisclosed herein generally refers to any configuration of a filter and afan to provide the functionality disclosed herein.

The air filtration systems 30 may be portable. Accordingly the supportstructure 32 may be coupled to a plurality of wheels 48 that can movethe air filtration system 30 to any desired location. Alternatively, theair filtration system 30 may be fixed and not portable. For example, asshown in FIG. 6, the air filtration system 30 may be installed in aceiling of a room such that the air outlet 36 is pointing generallydownward into the room. As will be described in detail in the following,FIGS. 1-7 illustrate several exemplary configurations by which the airfiltration system 30 may be designed to provide unidirectional orlaminar air flow from the air outlet 36. Regardless of what type andconfiguration of air filtration system 30 is used, the diffusion screen40 can be attached to the air outlet 36 of any air filtration system 30so as to provide unidirectional or laminar flow from the air outlet 36.

Referring to FIG. 1, the air filtration system 30 includes the supportstructure 32 having a base 60, a pair of upright beams 62 and an uppersupport 64. The base 60 is supported on the ground by the plurality ofwheels 48 so that the entire support structure 32 can be portable. Theenclosure 34 is attached to the upper supports 64, such that the airoutlet 36 is generally pointed downward to provide the air flow 46 inthe downward direction. The length of the upright beams 62 may beadjustable to provide height adjustability of the support structure 32.The enclosure 34 also includes an air flow inlet 66 that provides air tothe filter and the fan (not shown) that is housed in the enclosure 34.The diffusion screen 40 is attached to the enclosure 34, such that itcovers the air outlet 36 and provides the unidirectional or laminar airflow 46. A pre-filter 49 (shown in FIG. 1) may also be disposed in oroutside the enclosure 34 to provide pre-filtering of the air from theair flow inlet 66. Laminar flow is a state of flow where fluid at lowvelocities flows without lateral mixing, which is describedmathematically by a Reynolds number. The adjacent layers of flow slidepast one another like playing cards. Laminar flow is used inapplications such as forming fog screen for image projection ordesigning aircraft wings. Unidirectional flow is a state of flow wherefluid flows in a single direction with generally parallel streamlines,which is not constrained by specific Reynolds number ranges.Unidirectional flow is used in a number of applications such as cleanrooms for electronic and pharmaceutical industries and biological safetycabinets where process or products can be protected.

The diffusion screen 40 may include a plurality of releasable fasteners70 that can attach the diffusion screen 40 to the enclosure 34. Theenclosure 34 may be fixedly attached to the upper support 64.Accordingly the direction of the air flow 46 may not be adjustable.However, as shown in FIG. 4, the enclosure 34 may be pivotable relativeto the upper support 64 or the upright beams 62, such that the directionof the air flow 46 can be adjusted as desired.

FIGS. 4, 7 and 8 illustrate two applications in which the air filtrationsystem 30 of FIGS. 1, 4, 7 and 8 can be used. The air filtration system30 can be used in medical facilities where providing unidirectional orlaminar air flow over a patient is necessary to insulate the patientfrom the possibly unclean air in the room. Accordingly, as shown inFIGS. 4 and 7, the air filtration system 30 of FIG. 1 can be moved sothat the enclosure 34 is either directly over a bed 65 in which thepatient lies. Also, as shown in FIG. 4, the enclosure 34 can bepivotally mounted to the upright beams 62 at hinges 63 so as to adjustthe direction of the airflow 46 without having to move the airfiltration system 30. Such a portable air filtration system 30 can beeasily moved throughout a medical facility.

Referring now to FIG. 8, another application in which the air filtrationsystem of FIG. 1 can be used is shown. In certain work environments, itmay be necessary to shield a work surface 67 from the air surroundingthe work surface 67. Accordingly, the air filtration system 30 of FIG. 1can be moved so that the enclosure 34 is positioned over the worksurface 67 and the air flow 46 is directed generally downward onto thework surface 67. From the above examples, one of ordinary skill in theart will appreciate the numerous applications for which the disclosedair filtration system 30 may be used.

Referring to FIGS. 2, 3 and 5, examples of an air filtration system 30,where the filter and the fan (not shown) is disposed outside theenclosure 34, are shown. The filter and the fan (not shown) can behoused in a housing 71 that is supported on the ground with a pluralityof wheels 72. The housing 71 is an air flow communication with theenclosure 34 by an air flow conduit 74. Air flow from filter and the fan(not shown) flows through the air flow conduit 74 to reach the enclosure34 to then exit from air outlet 36 as the unidirectional or laminar airflow 46. The enclosure 34 may be supported by the air flow conduit 74.Accordingly, the air flow conduit 74 may be rigid to provide such asupport. Alternatively, the air flow conduit 74 may be flexible suchthat the enclosure can be supported by another structure to which it canbe attached.

The air filtration system 30 of FIG. 2 is portable and can be moved toany desired location. As described above, the air filtration system 30of FIG. 2 can be used for numerous applications where cleanunidirectional or laminar air is desired over a certain area. Referringto FIG. 5, if the enclosure 34 can be supported in an elevated position,the air flow conduit 74 may be flexible so as to provide moreflexibility as to how the air filtration system 30 can be used. Forexample, a flexible air flow conduit 74 can provide pivoting of theenclosure 34 so that the air flow 46 is directed to any desiredlocation. Also, because the air flow conduit 74 may be flexible, thehousing 71 can be moved relative to the enclosure 34. Such flexibilityin the position of the housing 71 with respect to the enclosure 34 andthe variability of the angle of the air flow 46 may be necessary incertain applications. As shown in FIG. 5, the enclosure 34 can bemounted over the work surface 67 to provide the air flow 46 generallydownward onto the work surface 67. Because the air flow conduit 74 isflexible, the housing 71 can be moved with the wheels 72 to any locationnear the work surface that is allowed by the flexibility and the lengthof the air flow conduit 74.

The air filtration systems 30 of the present disclosure may also includean air conditioning device (not shown) to provide conditioned air flowfrom the outlet 36. The air conditioning device, which may be a typicalair conditioning unit, a heater, or a humidifier can provide temperatureand relative humidity control to the clean air for comfort. The airfiltration system 30 may also include a flow conditioning device toprovide conditioned air flow from the outlet 36. The flow conditioningdevice, which may be a perforated plate or a series of straighteningvanes, can modify the air flow pattern prior to the diffusion screen toenhance the effectiveness of the diffusion screen.

Referring to FIG. 3, any one of the air filtration systems 30 disclosedherein may include an air return 80 that may be generally locatedopposite the air outlet 36 so as to capture the air flow 46 and returnthe air flow 46 to the filter and the fan (not shown). The air return 80may be connected to the filter and the fan (not shown) with a return airconduit 82. To support the return air conduit 82, an air return supportbase 84 may be provided. The air return support base 84 can be supportedon the ground with a plurality of wheels 86. Accordingly, the entire airfiltration system 30, including the air return 80 and the air returnconduit 82, can be portable and can be moved to any desired location.The air return 80 can also be pivotable about the hinge 85. Accordingly,the air return 80 can be pointed in a direction so as to capture a largevolume of the air flow 46.

The air return 80 can include a pre-filter 87 to clean the captured airprior to conveying the captured air back to the filter and the fan (notshown). Instead of or in addition to the pre-filter 87, the air return80 can also include a perforated plate 89. Because the air return 80captures some if not most of the air flow 46, the filter and the fan(not shown) will receive substantially cleaner air than if outside airwere drawn into the filter and the fan (not shown) from an air inlet.Although the air return 80 and the air return conduit 82 is shown withrespect to the air filtration system of FIG. 3 wherein the filter andthe fan (not shown) are in the housing 71 and not disposed in theenclosure 34, one of ordinary skill in the art will appreciate that theair return 80 can be used for air filtration systems 30 such as thoseshown in FIGS. 1, 4, 7 and 8 where the enclosure 34 also houses thefilter and the fan (not shown). If used with the air filtration systemof FIGS. 1, 4, 7 and 8, the return air conduit 82 can simply connect theair return 80 to the enclosure 34 so that the air flow 46 can becaptured and delivered to the filter and the fan (not shown).

Referring to FIGS. 9 and 10, the diffusion screen 40 is shown in moredetail. The diffusion screen 40 is generally configured to attach to theair outlet 36 and cover the air outlet 36 of any type of air filtrationsystem including the disclosed air filtration system 30. The diffusionscreen 40 is attached to the air outlet 36 of the enclosure 34 with oneor more releasable fasteners 70. The diffusion screen 40 includes thediffusion layer 44 and can be replaced when desired. Such a replacementmay be necessary when the diffusion screen 40 needs to be repaired,cleaned or discarded and replaced with a new diffusion screen 40.Additionally, such a replacement may be necessary when a diffusion layerthat provides a different air flow characteristic is desired. As shownin FIG. 10, a gasket 90 can be disposed between the diffusion screen 40and the air outlet 36 so as to provide a leak-free fit between thediffusion screen 40 and the enclosure 34.

Referring to FIGS. 11( a) and 11(d), several configurations of thediffusion layer 44 are shown. The diffusion layer 44 can include asingle layer of a diffusion fabric 92 that includes a weave pattern toprovide the unidirectional or laminar air flow 46 out of the air outlet36. As shown in FIG. 11( a), the diffusion fabric 92 may be disposed atthe bottom portion of the diffusion screen 40 so that it is spaced apartfrom the filter (not shown). In contrast, with reference to FIG. 11( b),the diffusion fabric 92 can be disposed at the upper part of thediffusion screen 40 so as to be adjacent to filter (not shown).Referring to FIGS. 11( c) and 11(d), the diffusion layer 44 may alsoinclude several layers of the same or different diffusion fabrics 92 toprovide a desired air flow 46 directed outward from the air outlet 36.For instance, the diffusion fabric 92 could provide unidirectional orlaminar flow from the air outlet 36. The diffusion fabric may bereplaceable so that it can be removed for cleaning or replacement.

The releasable fastener 70 for attaching the diffusion screen 40 to theenclosure 34 may be any type of fastener that can provide releasableattachment. Referring to FIG. 12, an example of a releasable fastener 70as shown. The releasable fastener 70 can include a latch 100 that isdisposed on the frame 42 of the diffusion screen 40. Enclosure 34 mayinclude corresponding latch keepers 102 so that the latches 100 engagethe latch keepers 102 and can provide secure fastening of the diffusionscreen 40 to the enclosure 34, with the ability to release the diffusionscreen 40 from the enclosure 34. Referring to FIGS. 13( a) and 13(b),two examples of latches 100 and latch keepers 102 are shown. Referringto FIGS. 14( a)-14(c), the latches 100 on the diffusion screen 40 mayengage a feature of the enclosure 34 such as a lip or a flange 104.Three examples of such a lip or flange 104 are shown in FIGS. 14(a)-14(c). The latch 100 may include a hooked end 106 that can engagewith the lip or the flange 104 to secure the diffusion screen 40 to theenclosure 34. The diffusion screen 40 may include only one latch or aplurality of latches 100, and because the enclosure 34 need notnecessarily include latch keepers 102, the latches 100 can engage a lipor flange feature of the enclosure 34 to fasten the diffusion screen 40to the enclosure 34.

The diffusion layer 44 can have either a single layer of the diffusionfabric 92 or multiple layers of the diffusion fabric 92. The multiplelayers of diffusion fabric 92 can be two layers of identical fabrics,the same fabric with the same pore sizes, or it can be two layers of thesame or different fabrics with different pore sizes. Severalcharacteristics of the diffusion layer 44 can influence the air flow 46.As described above, single or multiple layers of diffusion fabric 92 andtheir corresponding pore sizes can influence the characteristics of theair flow 46. Additionally, the space between each diffusion fabric 92and the space between diffusion layer 44 and the filter (not shown) mayalso influence the characteristics of the air flow 46. The pore sizes ofthe fabric layers, the weave patterns, and the constituent materials ofeach diffusion fabric 92 can be selected to provide specific flowcharacteristics that are desired, such as a unidirectional flow orlaminar flow.

In one example of the diffusion screen 40, a one-layer diffusion screenspaced 1-¾ inches apart from filter face performed better than when itwas about ⅝ inch apart from filter face. A two-layer diffusion screenwith the 1st layer about ⅝ inch apart from filter face and about 1-⅛inches apart from the 2nd layer underperformed a one-layer diffusionscreen with layer 1-¾ inch away from filter face. In another example ofthe diffusion screen 40, a two-layer diffusion screen with two differentpore size layers can perform differently if switching the 1st and 2ndlayers. When a plain weaved polymeric fabric sheet with a nominal poresize of 150 micrometers is used in a single diffusion layer screen, itdemonstrated less lateral flow or better unidirectional flow in flowvisualization than a diffusion screen using the same material with 250micrometer pore size. Depending on the application condition and desiredflow, experiments with various combinations of diffusion materials andlayers can be conducted to get an optimal or better setup. For instance,for air flow rates of about 90 feet per minute at filter face, aone-layer diffusion screen, made with plain weaved polymeric fabric withpore sizes of around 50 to 200 micrometer range and spaced apart about1-¾ inches from filter face, may significantly improve theunidirectional flow pattern. Therefore, the clean air can travel muchfurther to the desired area without containment due to minimalcross-contamination than clean air from a filter without diffusionscreen. The above-described characteristics of the diffusion screen 40are only exemplary and are not a limitation to the variety ofcharacteristics that can be employed to provide a desired type of flow.

The disclosed air filtration. system 30 can be used in any environmentwhere removal of certain particles, gaseous matter, or contaminatematter from the air is desired. The disclosed air filtration systems 30can be used in commercial and public facilities such as clean rooms andhospitals. Additionally, the air filtration systems 30 can be used inprivate homes for persons who suffer from asthma, allergies, andemphysema. The portability, small size, and the ability to remove thediffusion screen 40 for cleaning, repair, or to change flowcharacteristics makes the use of the disclosed air filtration system 30possible for residential and private use. However, one of ordinary skillin the art will readily appreciate that the features and functions ofthe disclosed air filtration system 30 also provide flexibility whenused in a commercial or public facility.

Furthermore, while the particular preferred embodiments have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from theteaching of the disclosure. The matter set forth in the foregoingdescription and accompanying drawings is offered by way of illustrationonly and not as limitation. The actual scope of the disclosure isintended to be defined in the following claims when viewed in theirproper perspective based on the related art:

1-44. (canceled)
 45. A mobile air filtration system comprising: (a) an enclosure assembly comprising: (i) an enclosure including an air inlet and an air outlet; (ii) a screen frame operatively coupled to the air outlet of the enclosure; and (iii) a unidirectional flow screen spanning the screen frame, the unidirectional flow screen having a downstream side defined along a single plane, the unidirectional flow screen covering the air outlet of the enclosure to result in unidirectional filtered air flow; the unidirectional flow screen: (1) including at least a single layer of material constructed and arranged to provide unidirectional filtered air flow from the air outlet such that filtered air flows in a single direction with generally parallel air streamlines; and (2) creating only unidirectional parallel air streamlines across the flow screen, to shield an area from unfiltered air surrounding the area to result in filtered air that travels further to the area with lower levels of cross-contamination from particulates present in the surrounding unfiltered air than filtered air from an air filtration system without a unidirectional flow screen; (b) a mobile housing unit comprising: (i) a housing having an air inlet and an air outlet, the housing being movable relative to the enclosure; (ii) an air filter positioned between the air inlet and outlet; and (iii) a fan positioned within the housing; and (c) an air flow conduit operatively connecting the mobile housing to the enclosure assembly.
 46. The mobile air filtration system of claim 45, wherein the unidirectional flow screen comprises two layers of material.
 47. The mobile air filtration system of claim 46, wherein the two layers of material are a fabric material.
 48. The mobile air filtration system of claim 47, wherein the fabric material has a weave pattern.
 49. The mobile air filtration system of claim 48, wherein the weave pattern is a plain weave pattern.
 50. The mobile air filtration system of claim 49, wherein the weave pattern has pore sizes of no greater than 250 micrometers.
 51. The mobile air filtration system of claim 49, wherein the weave pattern has a nominal pore size of 150 micrometers.
 52. The mobile air filtration system of claim 45, wherein the air flow conduit is flexible.
 53. The mobile air filtration system of claim 45, wherein the air flow conduit is rigid.
 54. The mobile air filtration system of claim 53, wherein the mobile housing unit is located on a floor of a space served by the air filtration system.
 55. The mobile air filtration system of claim 54, wherein the enclosure is supported by the rigid conduit.
 56. The mobile air filtration system of claim 45, further comprising a return air conduit connected to the air inlet of the mobile housing unit.
 57. The mobile air filtration system of claim 45, wherein the filter is constructed and arranged to remove particulate matter, gaseous matter, and/or contaminate matter.
 58. An air filtration system for providing unidirectional filtered air to a desired zone; the air filtration system comprising: (a) a support structure; (b) an enclosure coupled to the support structure and including an air outlet; (c) an air filter in communication with the air outlet; (d) a fan operatively coupled to the enclosure; (e) a screen frame; and (f) a unidirectional flow screen spanning the screen frame, the unidirectional flow screen having a downstream side defined along a single plane, the unidirectional flow screen covering the air outlet to result in unidirectional filtered air flow; the unidirectional flow screen: (i) being spaced from and parallel to the air filter; (ii) comprising multiple layers of polymeric fabric constructed and arranged to provide unidirectional filtered air flow from the air outlet such that air flows in a single direction with generally parallel air streamlines; (iii) having a weave pattern having pore sizes of no more than 250 micrometers; and (iv) resulting in only unidirectional parallel air streamlines across the flow screen to shield a work area from unfiltered air surrounding the work area.
 59. An air filtration system according to claim 58, wherein the multiple layers include two layers of identical fabrics.
 60. An air filtration system according to claim 58, wherein the multiple layers include two layers of fabrics, with each layer having a different pore size.
 61. An air filtration system according to claim 58, wherein the unidirectional flow screen has a first layer of fabric spaced ⅝th inch from the air filter.
 62. An air filtration system according to claim 61 wherein the unidirectional flow screen has a second layer of fabric spaced 1⅛th inch from the first layer of fabric.
 63. An air filtration system according to claim 58 wherein the multiple layers include two layers of different fabrics.
 64. An air filtration system according to claim 58, wherein the support structure is constructed and configured to be mobile.
 65. An air filtration system according to claim 64, wherein the support structure comprises a plurality of wheels.
 66. An air filtration system according to claim 65, wherein the enclosure is movable with respect to the support structure.
 67. An air filtration system for delivering a unidirectional filtered air flow to shield a work area from unfiltered air, the air filtration system comprising: (a) a unit comprising: (i) a support structure; (ii) an enclosure coupled to the support structure and including an air outlet; (iii) an air filter housed in the enclosure; (iv) a fan operatively coupled to the enclosure; and (b) a unidirectional flow screen having a downstream side defined along a single plane, the flow screen being positioned to cover the fan filter unit outlet and spaced away from and parallel to the filter, the unidirectional flow screen comprising: (v) at least one layer of polymeric fabric having a weave pattern with pore sizes of 50-250 micrometers, the at least one layer being constructed and arranged to provide only unidirectional filtered air flow from the fan filter unit across the flow screen such that the filtered air flows to the work area in a single direction with generally parallel air streamlines; (c) wherein cross-contamination of the filtered air flow by particulates present in the surrounding unfiltered air is less than that of an air filtration system having a fan filter unit without a unidirectional flow screen.
 68. An air filtration system according to claim 67, wherein the filtered air flow is laminar and has a velocity of about 90 feet per minute.
 69. An air filtration system according to claim 67, wherein the unidirectional flow screen is spaced 1¾ inches from the fan filter unit filter.
 70. An air filtration system according to claim 67, wherein the support structure is constructed and configured to be mobile.
 71. An air filtration system according to claim 70, wherein the support structure comprises a plurality of wheels.
 72. An air filtration system according to claim 67, wherein the enclosure is movable with respect to the support structure. 